Field of the Invention
The present invention relates to a plastic optical component used in optical apparatuses such as digital cameras and copy machines, and to a method for manufacturing the plastic optical component.
Description of the Related Art
There is a growing demand for the manufacture of thick optical components by an injection molding process. However, as the thickness of an optical component is increased, a difference in curing shrinkage occurs between the surface plastic layer that is first cured in the molding process and the inner plastic portion that is cured later and thus stress is increased in the optical component. This undesirably causes voids to be formed within the optical component or the internal stress to remain. The time for cooling such a thick optical component in a die is sharply increased due to the increase in the thickness of the optical component, and accordingly, the molding cycle increases remarkably.
In order to solve these issues, Japanese Patent Laid-Open No. 8-187793 proposes that a base member be integrated with plastic covering portions so that first and second surfaces of the base member are covered with the covering portions.
A thick plastic optical component must allow for a deformation resulting from the moisture absorption of the plastic thereof, and is accordingly formed of a plastic whose water absorption is low small. Otherwise, the surface of the optical component is likely to be deformed by moisture absorption and, consequently, the focus position may be displaced or other optical properties may be degraded. Unfortunately, the surface hardnesses of low-water-absorption plastics used for injection molding are generally low. Thus, low-water-absorption plastics may not be able to satisfy the abrasion resistance required for use for an exposed portion of a digital camera. In use in a copy machine, a thick plastic optical component may be damaged during manufacture or maintenance. Even the above-cited Japanese Patent Laid-Open No. 8-187793 cannot solve this issue because the base member and the plastic covering member are made of the same material.